The invention relates to a seatbelt lock having a preventive tensioning device.
German patent document DE 199 61 799 A1 discloses a seatbelt lock equipped with a preventive tensioning device. If a critical driving situation is sensed, an electric motor brings the seatbelt lock into a lowered intermediate position for about 5 seconds, during which an energy accumulator acts counter to the direction of the electric motor, so that, if no crash occurs it returns the seatbelt lock from the intermediate position to the operating position. If a crash occurs, the preventive tensioning device is actuated pyrotechnically in order to ensure higher restraining forces.
A disadvantage of this device is that after a crash the energy accumulator acts against the return force of the pyrotechnic tensioning device, so that locking means are necessary for the energy accumulator. In other words, the seatbelt lock has to lock from the start of a counterforce on the seatbelt lock which is greater than the tensioning force.
Therefore one object of the invention is to provide a seatbelt lock having a preventive tensioning device whose restraining force remains virtually constant over the entire course of the crash.
According to the invention, a preventive tensioning device is provided which enables a seatbelt lock to be transferred from an operating position into a lowered safety position by an energy accumulator which is maintained preloaded. The return from the safety position to the operating position is performed by a drive unit which is activated when no accident has taken place. The reversible arrangement has the advantage that a high tensioning speed of the seatbelt lock by the energy accumulator is possible, so that belt slack can be removed within the shortest possible time from the belt system in a critical driving situation. If it has small dimensions, the drive unit can be connected to a large transmission in order to produce the force necessary for the return of the seatbelt lock.
The tensioning device can be designed in such a way that the seatbelt lock can additionally be moved from the operating position into a raised comfort position with respect to the operating position. The advantage of this is that, in spite of the sunken arrangement of the seatbelt lock, something which is particularly customary in rear seats, accessibility of the seatbelt lock is improved, while maintaining the preventive safety function. The tensioning device therefore simultaneously performs the function of a seatbelt lock feeder. One advantage of this arrangement is that the seatbelt lock can be arranged in a very low-lying position relative to the seat cushion even in its operating position. This fundamentally improves the restraining action of the belt system, since the belt-branching point is to be arranged as low as possible between the lap and shoulder belt.
In a cost-effective embodiment, the drive unit not only returns the seatbelt lock from the safety position to the operating position, but at the same time transfers the seatbelt lock from the operating position into the comfort position.
In a simple embodiment, the energy accumulator may be designed as a compression spring which is maintained preloaded in a housing and is connected to the seatbelt lock via a draw-in cable. In the case of a critical driving situation, the compression spring is activated, so that it expands in the housing and takes the seatbelt lock along with it via the draw-in cable. However, it is also possible to employ a hydraulic or pneumatic energy accumulator.
In one embodiment, a rack may be fastened to the seatbelt lock and is driven by a corresponding gear of the drive device.
The drive unit may be an electric motor, which is present anyway (for example the electric motor which drives a seat adjuster); or may be a hydraulic pump.
A deflection unit is provided in order to transfer the seatbelt lock into the safety position or into the comfort position. This deflection unit comprises a shaft with a cam track in which a catch engages. Depending on whether or not the catch is in engagement, the shaft is locked or released. Furthermore, a ratchet gear may be provided with a grooved track which is likewise in engagement with the catch.
If a critical driving situation is detected, the compression spring is released, so that the draw-in cable drives the ratchet gear. The engagement between the catch and grooved track is configured geometrically in such a way that, during a preventive operation, the catch slips over the engagement with the grooved track, so that the ratchet gear transmits its movement to the shaft.
If the critical driving situation is not followed by a crash, the shaft and the cam track are driven in the opposite direction by the motor, and the spring is thereby reloaded. However, that only takes place if the catch is not in engagement with the cam track.
If a crash occurs, high tensile forces act on the seatbelt lock. As a result, the ratchet gear is driven, specifically in such a way that the synchronization between the cam track and grooved track is canceled. The catch comes into engagement and thus prevents the spring's being loaded by the high tensile forces.
In order to ensure that the seatbelt lock locks in every position as soon as the tensile force on the seatbelt lock is greater than the tensioning force, a synchronizing unit is provided. In one embodiment, the synchronizing unit comprises locking blocks which are mounted so that they can be rotated relative to one another within the housing for the spring.
Advantageously, the end faces of the locking blocks are designed as tooth flanks in order to realize a drive for the rotary movement of a locking block within the housing.
In a second embodiment, spiral hubs are arranged on a shaft, it being possible by displacing the spiral hubs toward one another to transmit a torque to a ratchet gear.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.